In such a field effect transistor, it is known that a transient variation in channel current occurs due to a variation of drain voltage. This phenomenon causes an unstable operation of device, for example, a frequency dispersion of drain conductance.
The above-mentioned transient variation is generally considered as a response at the deep level of a buffer layer or substrate, and a quantity and a time constant of the variation is dependent on the conductivity of buffer layer or substrate and the characteristic of the deep level.
Up to the present, to suppress such a transient variation, a conductive layer with an opposite conductive type to a channel layer is formed under the channel layer, and the conductive layer is short-circuited with a source or drain electrode to fix the potential(for example, Japanese patent application laid-open No.64-59961).
However, in the conventional field effect transistor, since the ohmic electrode contacted with the second conductive layer is short-circuited with the source or drain electrode, i.e., the device has an asymmetrical structure, the interchanging between the source electrode and the drain electrode causes the changing of characteristic. Thus, there rises a problem that it is difficult to design a circuit by employing such a field effect transistor.